1. Field of the Invention
Embodiments relate to a thin film transistor, a light emitting display device having the same and associated methods.
2. Description of the Related Art
A semiconductor layer using amorphous silicon or polysilicon has recently been developed for use in a thin film transistor (TFT) for light emitting display devices such as organic light emitting display devices, which use organic light emitting diodes (OLEDs) to emit light.
When the semiconductor layer is formed of amorphous silicon, the semiconductor layer may exhibit low mobility, and it may be difficult to use such a low mobility layer as a drive circuit of a display panel that requires a fast response time. Polysilicon may provide high mobility, but the threshold voltage of the TFT may not be uniform. Additionally, leakage current may occur in the amorphous silicon or polysilicon semiconductor layer when it is irradiated by light, e.g., light from a backlight unit.
A zinc oxide (ZnO)-based semiconductor may exhibit a band gap of 3.4 eV, which is higher than the light energy in a visible light region. Accordingly, a ZnO-based semiconductor may exhibit little or no leakage current resulting from visible light absorption. However, contact resistance (Rc) may be increased when using such a semiconductor, since a Schottky barrier may be formed due to differences in work function between the ZnO-based semiconductor and a material used to form source and drain electrodes in contact therewith. Accordingly, there is a need for a TFT in which a contact resistance between a ZnO-based semiconductor and a source/drain electrode material is reduced.